Lake Hongze is the fourth largest freshwater lake in China. The lake’s northwest shore is the provincial border of Jiangsu and Anhui and the rest are surrounded by two Jiangsu’s cities, Suqian and Huai'an.

In its history, the lake was much smaller in the 11th century and then was enlarged four times bigger (around 1,960 sq km) than the original size when Yellow River changed its course, forcing its water into Huaihe River, and together the water of the two rivers pooled up into the lake. After the Yellow River changed back to its regular course in1897, the Huaihe River was no longer able to go through its old path into the sea. Instead it continues pooling up into Lake Hongze.

The main water source of the lake is from Huaihe River and its main outlet runs southwards to the Yangtze River or via Grand Canal. And many artificial canals have been built in the past fifty years to drain the lake’s water to irrigate the nearby farmland and the most famous system is “North Jiangsu Irrigation Main Channel”. The irrigation system improves greatly the vulerable lake to contron flooding. Two major water exits of the lake are Sanhe River and North Jiangsu Irrigation Main Channel.